Researchers develop printable lasers

LONDON – Scientists from the University of Cambridge have reported a way of making organic lasers using inkjet printing technology. The breakthrough has implications for a wide range of potential applications from disposable lab-on-film test kits to arrays of colored lasers for low-cost emissive displays.

The research, reported in the journal Soft Matter, included the fabrication of arrays of lasers created by inkjet deposition of dye-doped chiral nematic liquid crystals. These materials, similar to the materials used between front and back plates in liquid crystal displays have the ability to self-assemble after deposition.

The team was able to show that the printing process itself can achieve
the necessary alignment for lasing action normal to the substrate. The
paper provides the laser threshold and linewidth characteristics of the
material.

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The research has shown that the helical way in which the liquid crystal molecules align one above the other, like the treads of a spiral staircase, can be used to create an optically resonant cavity. The team has now added a fluorescent dye and this means that the cavity can be optically excited to produce laser light.

Liquid crystal lasers have been produced before but only by filling a gap of about 10 microns between two accurately aligned glass plates and using polymer layers to align the crystals – an extension of LCD technology.

The team of researchers, drawn from the Centre for Molecular Materials for Photonics and Electronics and the Inkjet Research Centre, both within the department of engineering at the University of Cambridge, have devised a way to align the LC molecules and produce high resolution multi-colour laser arrays in one step, by printing them.

Suitable substrates are restricted to glass and silicon at present and the process remains complex and requires cleanroom conditions.

Using a custom inkjet printing system, the researchers printed hundreds of liquid crystal dots on to a substrate covered with a wet polymer solution layer. As the polymer solution dries, the chemical interaction and mechanical stress cause the liquid crystal molecules to align and turn the printed dots into individual lasers. However, the process could be extended to almost any surface, rigid or flexible, and eventually applied with existing standard printing equipment, the researchers have said.

A U.K. patent application has been filed with the help of Cambridge Enterprise, a subsidiary of the University of Cambridge which is responsible for making commercialization arrangements for technologies discovered at the university.